Issue 29

M. Scafè et alii, Frattura ed Integrità Strutturale, 29 (2014) 399-409; DOI: 10.3221/IGF-ESIS.29.35 405 Sample ID Number σ max UD (A) σ max UD (B) σ max UD (C) σ max UD (D) 1 151.1 138.6 139.8 126.3 2 139.4 147.6 139.1 130.8 3 143.3 141.3 138.8 140.4 4 146.5 142.4 135.4 132.2 5 139.9 143.3 150.7 131.4 6 167.8 147.6 125.8 138.9 7 140.4 149.3 146.3 133.2 8 146.8 140.7 135.7 138.3 9 156.6 144.8 136.7 142.0 10 159.5 141.6 137.1 145.2 11 156.9 138.8 134.7 142.8 12 156.1 134.9 141.2 130.8 Mean Value 149.8 143.3 138.2 136.5 Std. Deviation 9.3 3.6 6.4 6.0 CV % 6.2 2.5 4.6 4.4 Table 8 : UD lamina compressive strengths obtained through Back out Factor (normalized results) Finally, the results of the mechanical characterization, in terms of mean values of compressive strength with their standard deviation, are summarized in Tab. 9. These values are in agreement with data reported in the datasheet of the prepreg material used for lamination. Parameters Experimental characterization results 0° Compressive Strength (cross-ply A) 149.8 ± 9.3 0° Compressive Strength (cross-ply B) 143.3 ± 3.6 0° Compressive Strength (angle-ply C) 138.2 ± 6.4 0° Compressive Strength (angle-ply D) 136.5 ± 6.0 0° Compressive Modulus 96.6 ± 4.1 90° Compressive Strength 20.7 ± 0.5 90° Compressive Modulus 5.0 ± 0.3 Table 9 : Results summary: mean values and standard deviations of Compressive Strength and Modulus (normalized results). The data reported in Tab. 9 show that the compressive strength of the 0° lamina is greater if the estimate is done by cross- ply specimens. The maximum difference between angle-ply and cross-ply is of about 10%. In addition, the resistance values that agree better with those reported in the data sheet of prepreg, are those relating to cross-ply specimens. Finally, the cross-ply lamination is simpler than that of the angle-ply and the expression of the BF is considerably simplified in the first case than in the second. Then, the estimate of the 0° lamina strength, it’s better by use of cross-ply specimens [0°/90°] ns . As examples, in the following Fig. 1 and 2 the plots obtained from 0° UD compressive tests are shown. They represent the typical mechanical behaviour of these composite materials. Fig. 1 shows, as expected, that the behaviour is of elastic type up to failure and Fig. 2 shows that the % bending of the sample is limited up to failure.